U.S. Pat. No. 4,857,799 describes an example of conventional colour field emission display. Such displays typically comprise a cathodoluminescent screen overlying and spaced from a two dimensional matrix of field emission cathodes. U.S. Pat. Nos. 3,789,471, 3,665,241, and 3,775,704 describe examples of, and methods of producing such cathodes. Each cathode comprises three arrays of field emissive tips. The arrays each comprise substantially the same number of tips (typically 1000). The screen is divided into a plurality of pixels. Each pixel is divided into three subpixels. Each subpixel is formed by a phosphor corresponding to a different one of the three primary colours, Red, Green and Blue. Each array of a cathode faces a different subpixel of a corresponding pixel. The arrays are individual addressable via row and column conductors.
In operation, voltages determined by red, green and blue input video signals are sequentially applied to the row and column conductors to address each cathode in turn in a raster fashion. The voltages interact to generate a localised high electric field at each tip. The localised electric fields drag electrons from the tips. The electrons are collectively accelerated towards the phosphors by an electric field generated between the screen and the cathode matrix. The phosphors are excited by incident electrons to display an image as a function of the input video signals.
The three phosphors corresponding to each cathode in general have different Quantum Yields or Efficacies (typically 1.5 lm/w for red, 0.5 lm/w for green, and 4.0 lm/w for blue). Conventionally, therefore, the video signals each translated by separate algorithms into the voltages addressed to the arrays to maintain tracking between the primary colour components of a gray scale displayed image. In other words, the separate algorithms maintain the "Colour point" or "White point" of the image between extremes of the gray scale. This requirement leads to complex drive circuitry for addressing the voltages to the row and column conductors.